Construction affording automatic synchronizing of master and slave fluid power cylinders

ABSTRACT

An improved master cylinder in which the interior of the cylinder wall has a short longitudinal groove which causes the master and slave pistons to complete their strokes and do so at substantially the same time. The groove, located near end of cylinder, permits restricted flow past the master cylinder piston when this piston is nearing and at the end of its stroke thereby causing both master and slave pistons to complete their respective strokes. A similar groove at the other end of the cylinder performs similarly.

United States Patent Schmucker Sept. 3, 1974 [54] CONSTRUCTION AFFORDING 2,997,849 8/1961 Shimanckas 60/54.5 R AUTOMATIC SYNCHRONIZING OF :32? :Vflkmson 92/61 reese 2 35 2 2 32 SLAVE FLUID POWER, 3,583,282 6/1971 Cope 60/547 [75] Inventor: Loftin Waldean Schmucker, FOREIGN PATENTS OR APPLICATIONS Hutchinson, Kans' 137,775 1902 Germany 91/400 [73] Assignee: The Cessna Aircraft Company, Primary Examiner lrwin Cohen wlchlta Kans' Assistant ExaminerA. M. Zupcic 22 Filed; Oct 20 1972 Attorney, Agent, or FirmEdward L. Brown, Jr.

21 A 1. N 299 322 1 1 PP 0 57 ABSTRACT An improved master cylinder in which the interior of [52] US. Cl 60/546, 60/547, 919/3601, the cylinder wall has a Short longitudinal groove which [51] Int Cl Flsb 7/00 FSb 15/20 causes the master and slave pistons to complete their [58] Field 91/462 399 400 strokes and do so at substantially the same time. The /54 5 groove, located near end of cylinder, permits restricted flow past the master cylinder piston when this [56] References Cited piston is nearing and at the end of its stroke thereby causing both master and slave pistons to complete UNITED STATES PATENTS their respective strokes. A similar groove at the other 928,100 7/1909 Berry 91/399 end of the cylinder performs similarly. 966,601 8/1910 Rosenfelt et a1 91/399 1,749,924 3/1930 Runge et a1 91 402 3 Clwms, 6 Drawlng Flgures CONSTRUCTION AFFORDING AUTOMATIC SYNCIIRONIZING OF MASTER AND SLAVE FLUID POWER CYLINDERS BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a master fluid power cylinder capable of performing useful work while simultaneously controlling the coordinated operation of an associated slave cylinder which also performs useful work. In such a combination, it is often required that the pistons and rods of the two cylinders start their movement at the same time, travelat substantially the same velocity, and reach the ends of their respective strokes at substantially the same time. This is necessary, for example, when two such cylinders are used to raise and lower opposite ends of the reel on a combine which cuts, threshes and cleans grain as it moves over a field.

Conventional master and slave cylinders can be so proportioned that they will have uniform movement. However, unequal wear of the working parts, particularly the fluid seals, cause the cylinders to get out of synchronization. They are said then to be out of phase and the operation for correcting this condition is sometimes called rephasing. It shall be called synchronizing in this application.

2. Description of the Prior Art The present state of the art on synchronizing master and slave cylinders by affording a restricted flow past the master cylinder piston at the end of of its stroke is exemplified by US. Pat. No. 3,347,043, issued to Evans Glenn Freese.

The Freese patent requires cylinder walls having orifices and exterior fittings to interconnect the restricted orifices with the ports. This invention is an improvement effected by substituting a cylinder wall with a short inside groove for the orifices and exterior connections. This simplifies the cylinder construction and avoids projections, thereby reducing outside dimensions and eliminating some manufacturing operations and parts. Another problem, although not severe, is wear on the piston seal as it passes back and forth over the orifices. The longitudinal groove with rounded edges decreases wear on the piston seal.

SUMMARY OF THE INVENTION This invention more particularly concerns an improvement on the device used in the aforementioned Freese patent of affording restricted fluid communication between the rear and forward chambers of the master cylinder. In place of an orifice through the cylinder wall affording restricted exterior communication, my invention affords restricted interior communication between the chambers by means of a cylinder wall with a short longitudinal groove in the inside surface of the cylinder located adjacent to the piston at the end of its stroke. This groove is long enough to afford restricted flow around the piston seal thereby causing both pistons to reach the end of their stroke and to do so at substantially the same time. They therefore start the next stroke simultaneously. Such a groove can be used at each end of the pistons stroke if desired. The groove allows both pistons to reach the end of their strokes by either venting the excess fluid or supplying the shortage of fluid to the forward end of the master cylinder and to the connected slave cylinder.

It is an object of this invention to simplify the manufacture, reduce the cost and outside dimensions of a master cylinder that synchronizes its stroke with a slave cylinder.

It is a further object of this invention to reduce the number of fittings and parts.

Another object is to reduce the wear on the piston seal and ring caused by it passage back and forth over the orifices in the cylinder wall.

BRIEF DESCRIPTION OF DRAWINGS This invention will become more clearly understood when the following description is read in connection with the following drawings, in which:

FIG. 1 is a central longitudinal sectional view through a master cylinder embodying my invention, and schematically shown therewith is the power system and a slave cylinder connected in series;

FIG. 2 is an enlargement of a portion of FIG. 1 showing the groove and portion of adjacent piston with its seal;

' FIG. 3 is a fragmentary transverse section taken on the line 3 3 of FIG. 1 and showing a transverse section of the machined groove and cylinder wall;

FIG. 4 is similar to FIG. 3 but shows a machined groove with rounded edges;

FIG. 5 is similar to FIG. 2 but shows a machined groove with rounded ends; and

FIG. 6 is similar to FIG. 4 but shows a formed or stamped groove.

DESCRIPTION OF THE PREFERRED EMBODIMENT A cylinder construction which embodies my invention is shown in FIG. 1 and is designated as a whole by the numeral 10. For clarity in description, cylinder 10 is shown connected in series to a slave cylinder 14 by conduit 12. Cylinder 10 will be referred to herein as a master cylinder although it should be understood that this cylinder may be used as a double acting working cylinder without the slave cylinder.

Referring to FIG. 1, master cylinder 10 has cylinder wall 16, rear head 18, forward head 20, piston 24 and piston rod 40. The piston 24 is sealed against the inside surface 17 of cylinder wall 16 by a conventional piston ring 28 backed up by O-ring 26. O-ring 22 seals between rod 40 and forward head 20.

Rear port 50 connects fluid power source 54, through conduit 66, valve 62 and conduit 52 with rear chamber 34 of master cylinder 10. Conduit 58 connects power source 54 with reservoir 60.

Forward port 48 connects forward chamber 36 of master cylinder 10 with chamber 38 of a single acting slave cylinder 14. Slave cylinder 14 has piston 68 and piston rod 44.

It will be assumed that both piston rods 40 and 44 are operating against forces applied in direction of the arrows 42 and 46 respectively.

Forward groove 30 affords a very restricted amount of flow past piston ring 28 when piston 24 nears the outer end of its stroke. The increment of travel of piston 24, while still affording flow past the piston ring 28, can best be seen in FIG. 2. This restricted flow connection through groove 30 causes both master piston 24 and slave piston 68 to reach the forward end of their strokes. Any excess of fluid in slave chamber 38 and forward chamber 36 that would otherwise keep master piston 24 from reaching the outer end of its stroke passes through groove 30 to rear chamber 34. In like manner, if there is not sufficient fluid to fill chamber 38 and force slave piston 68 to the outer end of its stroke, groove 30 provides passage for sufficient fluid to flow from rear chamber 34 through forward chamber 36, forward port 48, conduit 12 into slave chamber 38, forcing slave piston 68 to outer end of its stroke.

The two pistons, 24 and 68, both reach the outer end of their stroke and do so at substantially the same time. Being at the end of their respective strokes, pistons 24 and 68 start their return strokes simultaneously when valve 62 is moved to let fluid flow from rear chamber 34 through rear port 50 and conduits 52 and 56 into reservoir 60.

Rear groove 32 performs a similar function when master piston 24 nears and arrives at the inner end of its stroke. Both master piston 24 and slave piston 68 reach the inner end of their respective strokes and do so at substantially the same time. Without some provision for correction, an excess quantity of fluid in front chamber 36 and slave chamber 38 would prevent slave piston 68 reaching the inner end of its stroke and a shortage of fluid would prevent master piston 24 from reaching the inner end of its stroke. Rear groove 32 provides a similar restricted flow past piston 24 to pass excess fluid to rear chamber 34 and out rear port 50; or lets master piston 24 move to complete its return stroke. Both pistons 24 and 68 are in proper position to begin their forward strokes simultaneously.

These grooves 30 and 32 afford a simple method of causing the pistons 24 and 68 to complete their strokes despite small differences in leakage or differences in loading forces 42 and 44. The corrections are confined to the ends of the stroke. The improvement in using the grooves 30 and 32 instead of orifices through the cylinder wall 16 lies in less machine work and welding and the elimination of exterior fittings.

FIG. 4 shows the groove 30 with rounded edges 70 to decrease the wear on piston ring 28. The rounded lingitudinal ends 72 in FIG. 5 similarly reduce wear on piston ring 28.

FIG. 6 shwos a groove 30" having rounded edges 70' which are stamped or formed in the cylinder wall 16 rather than machined.

What has been shown in FIGS. 2, 3, 4, S and 6 concerning groove 30 and described above, applies likewise to forward groove 32. Both rear groove 30 and forward groove 32 are alike in cross section, length, rounded edges and ends, and in their longitudinal location in reference to the position of piston 24 at the inner and outer ends of its stroke. Synchronization can be afforded at only one end of the stroke, if desired, by using a groove at that end only.

While not shown in the drawings, a plurality of smaller grooves around the inside periphery of the cylinder wall could be utilized in place of a single groove.

Having described the invention with sufficient clarity to enable those familiar with the art to construct and use it, I claim:

1. A fluid power cylinder utilized in a series circuit with a slave cylinder in a master-slave relationship, the power cylinder having a cylinder wall, forward and rearward heads attached to the ends of the cylinder wall, each head having a port therein for exterior fluid communication; a piston having a circumferential seal in a sliding contact with the inside wall of the cylinder wall dividing the cylinder into forward and rearward chambers, wherein the improvement comprises:

groove means longitudinally positioned on the inside surface of the cylinder wall approximate one end of the cylinder affording a limited flow path across the piston between the forward and rearward chambers when the piston is positioned at said one end of its stroke, the length of the groove means being slightly greater than the axial width of the piston seal and less than the axial width of said piston, the groove means having a sufficiently small crosssectional area and length to cause the power cylinder to remain in phase with the series connected slave cylinder at the beginning of the power cylinders stroke.

2. A cylinder as described in claim 1, in which the intersection of the groove surface with the inside surface of the cylinder is rounded to provide a smooth passage of the piston seal.

3. A cylinder as described in claim 1, wherein a second groove means is located approximate the other end of the cylinder wall whereby rephasing can be achieved at either end of the cylinder stroke. 

1. A fluid power cylinder utilized in a series circuit with a slave cylinder in a master-slave relationship, the power cylinder having a cylinder wall, forward and rearward heads attached to the ends of the cylinder wall, each head having a port therein for exterior fluid communication; a piston having a circumferential seal in a sliding contact with the inside wall of the cylinder wall dividing the cylinder into forward and rearward chambers, wherein the improvement comprises: groove means longitudinally positioned on the inside surface of the cylinder wall approximate one end of the cylinder affording a limited flow path across the piston between the forward and rearward chambers when the piston is positioned at said one end of its stroke, the length of the groove means being slightly greater than the axial width of the piston seal and less than the axial width of said piston, the groove means having a sufficiently small cross-sectional area and length to cause the power cylinder to remain in phase with the series connected slave cylinder at the beginning of the power cylinder''s stroke.
 2. A cylinder as described in claim 1, in which the intersection of the groove surface with the inside surface of the cylinder is rounded to provide a smooth passage of the piston seal.
 3. A cylinder as described in claim 1, wherein a second groove means is located approximate the other end of the cylinder wall whereby rephasing can be achieved at either end of the cylinder stroke. 